4pED8. A simple water-filled compliant-tube calibrator.

Several geometries for low-frequency underwater calibrations are in common
use, but often require either anechoic walls, rigid walls, or tanks (or lakes)
of large dimensions with respect to a wavelength. Such facilities are
frequently not practical for use in teaching laboratories either because of
inaccessibility or because the facility must be shared with active researchers.
The compliant, water-filled cylindrical tube described in this paper permits
low-frequency calibrations in a laboratory environment, with modest cost and
size. The sound speed inside one such device is approximately 300 m/s, which
allows 100-Hz measurements in tubes 1 m long. The limitations of the compliant
tube calibrator and examples of measurements made using the calibrator will be
discussed.